Interval training is a great way to condition your heart and build your endurance. I treat interval training sessions as my “quickie” workouts. Since you’re working harder during short bursts of energy, you don’t need to work out as long. This is my go-to interval training plan, which I do on the elliptical.
This workout will really get your heart rate up, so make sure that you finish with at least a 5 minute cool down.